The hydraulic chuck of this invention is an improvement upon the device shown and described in U.S. Pat. No. 4,393,945. In the device of that patent, a housing is mounted on a spindle rotated by a rotary table, the housing being held against rotation with the spindle, but being free to move axially with the table. A hollow chuck body is fixedly mounted on the spindle, for rotation therewith. A tube mounted on the chuck body has fingers extending axially to cam plungers out of engagement with a kelly bar extending through the spindle. The device has worked well, but it requires a substantial number of parts, the use of O-rings, and sealed bearings that can not easily be relubricated.
One of the objects of the invention is to provide a hydraulic kelly bar chuck that requires fewer parts than the device of U.S. Pat. No. 4,393,945, but operates as effectively.
Another object is to provide such a chuck in which bearings are cooled and lubricated by hydraulic fluid used to operate the chuck plungers.
Yet another object is to provide such a chuck in which a visual indication is given of the withdrawal of the plungers from engagement with the kelly bar.
Still another object is to provide a construction of plungers that minimizes wear and tends to insure engagement with the kelly bar in the course of forcing the kelly bar downward.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.